Pentavitus

[Arix]

Pentavitus
Creatures (17)
2 Memnarch
3 Dross Scorpion
4 Steel Wall
4 Vedalken Engineer
4 Pentavus

Non-creature spells (20)
2 Last Word
3 Crystal Shard
3 Thirst for Knowledge
4 Condescend
4 Fabricate
4 Gilded Lotus

Lands (23)
4 Darksteel Citadel
4 Seat of the Synod
15 Island

Yup, it's based around Pentavus. One of the main parts is the infinite mana combo of Pentavus + Dross Scorpion + Gilded Lotus, at which point I generally use Memnarch to steal everything. Last Word, though not the most efficient counterspell around, has saved me multiple times. Condescend is there for a little more protection and a small boost of manipulation to find the pieces. Fabricate can fetch a whole load of stuff, usually either whichever piece of the combo I'm missing, or if I have them all, a Crystal Shard. Crystal Shard itself can give me infinite 1/1 flying Pentavites once I have my infinite mana, while Thirst for Knowledge can help me find something if I need more than one card, or if I don't really need anything specific. Steel Wall is just there for some early defence before I get going.

The ideal opening play for this deck is -
Turn 1, land of any sort/Island.
Turn 2, land of any sort/Island, Vedalken Engineer.
Turn 3, land of any sort, Gilded Lotus.
Turn 4, land of any sort, Pentavus.
And go from there.

If you don't understand the infinite mana combo -
1. Tap Gilded Lotus for 3 mana of any colour.
2. Use 1 and remove a counter from Pentavus to make a Pentavite.
3. Use 1 and sac the Pentavite to put a counter back on Pentavus.
4. Sacking the Pentavite triggers Scorpion, allowing me to untap Lotus. Now I'm back where I started, with 1 extra mana in my mana pool.
5. Repeat as often as necessary.

If you don't understand the infinite Pentavite combo -
6. Create 4 Pentavites.
7. Use Crystal Shard to bounce Pentavus back to my hand.
8. Replay Pentavus, fresh with 5 counters.
9. Sac a Pentavite, allowing me to untap Shard. Now I'm back where I started, with 3 Pentavites.
10. Repeat as often as necessary.

One final point - yes, I did intentionally make it Mirrodin block only.

[lordmayhem]

Wouldn't Disciple of the Vault be a better kill condition?

Tap Gilded Lotus (add 3)
Use 1 to create pentavite
Use 1 to destroy pentavite
Disciple triggers.
Untap Lotus.

[Arix]

No. Disciple of the Vault is no fun. Besides, I want to keep it monoblue.

[Ephraim]

I've been thinking about this deck for a couple of days. It's definitely an interesting idea. As far as casual comboes go, I think you've gone in the right direction. It's clunky enough not to be abusive, at least in a casual dual. Any combo deck is going to be abusive in chaos. My recommendation would be to find some way to win besides Memnarch. He's frustrating to play against in a casual arena because even before you get the combo activated, he sits there and rudely takes the other players' key permanents. Sure, you have a right to protect yourself, but Memnarch is a very irritating way of doing so. Tower of Champions, for example, still maintains the fiction that your deck wins through combat, plus casual players are likely to appreciate an infinite army of infinitely large Pentavites more than they will appreciate you stealing all of their permanents.

[Arix]

You don't know what my group are like. Irritating stuff is the way we go. I do annoying stuff, everyone else does annoying stuff, it's the way we are. Besides, I don't have any Towers. Memnarch is the best way to go, and nobody even cares that I use him.

And the combo goes off with surprising frequency - there's rarely been a game where I haven't gotten all the pieces.